1. Field of the Invention
The present invention relates to a sampling inspection managing system for performing inspections of selected lots in a inspection step to check the processing result of a processing step in a semiconductor production line including plural processing steps and inspection steps. The sampling inspection is performed to check whether articles or products are good or defective at an inspection frequency suitable for an inspection purpose for each kind of article or product.
2. The Related Art of the Invention
A production line for semiconductor devices comprises plural processing steps such as a film forming step, a photolithography step, etc., and plural inspection steps such as a film thickness inspecting step, a development inspecting step, etc.
The number of wafers to be processed at one time in each processing step is dependent on the volume processing characteristics of an apparatus being used. For example, twenty five wafers may be set as one lot. In a batch process, plural lots are simultaneously processed when an apparatus having high volume processing characteristics is used. On the other hand, when an apparatus having low volume processing characteristics is used, a lot of wafers or one or several wafers are simultaneously processed. In each processing step, the apparatus to be used, the number of lots or wafers to be processed at one time, the processing conditions, the processing environment, etc., are set in advance in accordance wit the kind of products to be produced.
In each inspection step, the processing result of a processing step preceding the inspection step is checked. In the inspection step, articles or products (goods in process) are checked to determine whether the processing result is good or defective. A 100% inspection for all of the articles or products, or a sampling inspection for sampled articles or products, is made. For example, when a production line is started up to produce new model products or to change the production site, the 100% inspection is performed because no processing result data for processed goods exists for the production facilities, the production environment, and the production conditions. A 100% inspection contains a 100% lot inspection, a 100% in-lot wafers inspection, a 100% in-wafer chip inspection, and a 100% in-chip elements inspection. For example, in the 100% in-lot wafer inspection, all of twenty five wafers constituting one lot are inspected.
On the other hand, in the case of a production line in which production is continuously or intermittently carried out, for a processing step for which it has been confirmed that the production is to be continued with the current processing conditions, and that the working state of the apparatus is stable, or for a processing step for which the processing standards are not severe, it is unnecessary to perform the 100% inspection, thereby lowering the production efficiency, even while the sampling inspection is carried out in spite of the 100% inspection.
The sampling inspection contains a lot sampling inspection, an in-lot wafer sampling inspection, an in-wafer chip sampling inspection, an in-chip element sampling inspection, etc. In the in-lot wafer sampling inspection, a predetermined number of wafers located at predetermined positions are sampled from 25 wafers constituting one lot and inspected. For example, when the first processed wafer and the last processed wafer are inspected, the inspection processing time in the inspection step can be shortened to 23/25ths that of the 100% inspection.
When many types of articles are produced in a production line, there may be cases where there are two kinds of articles, one for which the processing standards are severe, and one for which the processing standards are not severe, or where there are two kinds of articles, one of which where sudden minute differences have a great effect, and one of which where sudden minute differences have little effect, existing in the same processing step, and where these different kinds of articles are continuously but irregularly (in term kinds) processed. In such a case, if the 100% inspection is carried out, this may be an undesired inspection due to the fact that it may lower the production efficiency. Further, if a sampling inspection is merely carried out at a frequency of once per several lots, some kinds of articles may be subjected to an undesired inspection, so that the production efficiency is lowered. Further, other kinds of articles for which the inspection would be originally required may be subjected to a next processing step without being subjected to the required inspection, so that the quality of the articles are lowered. Therefore, it has conventionally been required to develop a sampling inspection managing system for performing an inspection at a suitable inspection frequency that meets the specific inspection purposes for all kinds of products.
Japanese Laid-open Patent Application No. Hei. 11-291144 discloses and proposes one of these conventional inspection systems, and it is an inspection lot managing system having sharing means to which an IF-THEN type assortment rule containing events such as facility errors, switching of products, occurrence of maintenance work, etc., is applied. However, this publication neither discloses nor teaches a method of setting an inspection frequency in accordance with the kind of products.
The present invention has been implemented in view of the foregoing circumstances, and has an object to provide a sampling inspection managing system which can check the processing result (good or defective) of each processing step at a suitable inspection frequency that meets an inspection purpose for all kind of products.
In order to attain the above object, according to the present invention, a sampling inspection managing system for making an inspection to selected lot in a inspection step in order to confirm the processing result of a processing step in a semiconductor device production line including plural processing steps and inspection step, comprising : first means for setting whether each processing step is a step of determining a sampling inspection frequency in the specific inspection step; second means for setting the inspection frequency in the specific inspection step for each kind of production to be processed for the processing step which has been set as xe2x80x9cthe step for determining the sampling inspection frequencyxe2x80x9d in the first means; third means for counting the number of lots to be processed for each kind of product for the processing step which has been set as being xe2x80x9cthe step for determining the sampling inspection frequencyxe2x80x9d in the first means; and fourth means for judging on the basis of the lot number counted in the third means, whether each lot should be inspected in the specific inspection step, and for storing the judgment result as information of each lot.
In the sampling inspection managing system, the second means sets the inspection frequency so that a judgment on xe2x80x9cinspection is madexe2x80x9d or xe2x80x9cno inspection is madexe2x80x9d is set at a frequency of once per n lots, where n represents an integer.
In the sampling inspection managing system, the third means returns the lot number to be processed to zero, and starts new counting when the lot number counted is equal to the inspection frequency n preset by the second means.
In the sampling inspection managing system, for the processing step for which xe2x80x9cinspection is madexe2x80x9d is set at a frequency of once per n lots in the second means, the fourth means judges xe2x80x9cinspection is madexe2x80x9d for the lot which the processing lot number counted by the third means is equal to the inspection frequency n set by the second means while judging xe2x80x9cno inspection is to be madexe2x80x9d for the other lots, and then stores the judgment result.
In the sampling inspection managing system, for the processing step which xe2x80x9cno inspection is madexe2x80x9d is set at a frequency of once per n lots in the second means, the fourth means judges xe2x80x9cno inspection is madexe2x80x9d for the lot which the processing lot number counted by the third means is equal to the inspection frequency n set by the second means, while judging xe2x80x9cinspection is madexe2x80x9d for the other lots, and then storing the judgment result.
In the sampling inspection managing system in the case of a processing step in which plural lots are simultaneously processed, when plural lots to be simultaneously processed are set as one batch, the first means and the second means set a batch sampling frequency so that the judgment of xe2x80x9cinspection is to be madexe2x80x9d or xe2x80x9cno inspection is to be madexe2x80x9d is set at a frequency of once per m batches, where m represents an integer, and also set a lot which lot should be inspected in the batch which the judgment of xe2x80x9cinspection is to be madexe2x80x9d is set.